1. Technical Field
The present invention relates to electronic mail transmission and, more particularly, to the detection and blocking of unsolicited bulk electronic mail otherwise known as spam.
2. Description of the Related Art
There has been an increasing growth of electronic traffic over the Internet in recent years. As the Internet continues to evolve and traffic continues to grow, various problems begin to surface. One of the most notable problems today is that of unsolicited bulk email, or spam. Spam is generally in the form of marketing information that is transmitted to a large number of users without solicitation. This type of email is often useless to the person receiving it. Nonetheless, a great deal of time is spent by the recipient to open the email and review/delete the message. While it is possible that a small number of recipients may have an actual interest in the email, the vast majority have no interest and tend to delete spam upon receipt. The term spammer is often used to identify a person (or organization) who transmits spam.
One of the primary objections to spam is that it can waste valuable resources without proper authority. For example, spam can take up valuable storage space on an individual's (or company's) email account or mail server. This can often result in a storage quota being exceeded on the user's email account. When this happens, legitimate email can be prevented from reaching the user. For example, most internet service providers (ISP) allocate a certain amount of storage space for each user. Once that storage space is exceeded, email delivery is suspended. All email sent to the user during the suspension period is discarded, or otherwise not accepted by the ISP. Users must delete emails in their accounts in order to receive new emails.
Another problem with receiving spam is that a significant amount of time can be spent reviewing and deleting messages that have been received. Since a recipient may not know immediately whether a message is spam, the contents must be reviewed prior to making a decision to save or delete. Even if the message can be identified as spam from the header information, it must still be deleted by the user.
Certain types of spam can direct users to different web sites where time is ultimately spent reviewing advertising content. For example, a spam email can advertise discounts or sale from a particular merchant. Users must subsequently follow a link to the merchant's website in order to obtain more information. Once at the merchant's website, users are overwhelmed with product information and incentives which lead to surfing the merchant's website. While this does not pose a problem to home users, an employer can lose employee productivity during this time period. Another objection to the receipt of spam is that the messages tend to contain objectionable and/or illegal content such as pornography, illegal activities, financial scams, etc.
There are various methods in place to intercept, or counter, spam being transmitted to individuals. These methods attempt to filter, or block, email messages that are received from sources that have been identified as, and/or associated with, spammers. Email messages can also be blocked based on information contained in the message, such as the subject line. One problem associated with such techniques, however, is the fact that spammers can easily change the source of spam to bypass the filters. Furthermore, spammers continue to improve the content of their spam to make it difficult to filter. For example, some emails cannot be filtered without examining the content of the message, which may raise various legal and privacy issues. It is also difficult to determine exactly when a user (or system) is transmitting too much email to qualify such transmission as spam. Without such a determination, the spam transmitted cannot be filtered.
Some current methods of filtering spam involve manual selection of a threshold to identify a sender as a spammer. Such methods, however, are inefficient and difficult to implement due to the amount of email being transmitted on a daily basis. Furthermore, spammers can easily change the address being used to transmit spam. Consequently, there is a high cost associated with monitoring the level of email being transmitted by users in order to manually establish a threshold for classifying such messages as spam. Additionally, the time required to adjust the threshold may be too long, resulting in spammers changing their addresses prior to being blocked or immediately upon being blocked.